The invention relates to an autoconverter of the type described in U.S. Pat. No. 4,481,460, issued Nov. 6, 1984. A charging capacitor is connected to a dc source via a charging diode and a charging inductor. A charging switch is periodically closed by a signal from a control means with given pulse-duty factor. The charging switch periodically connects the charging inductor to the dc source. Two series connected alternately driven first and second switches are connected parallel to the charging capacitor. Means are provided for synchronizing the control means for the charging switch by a square wave voltage at the first switch such that the charging switch is closed when the first switch opens and is opened after a time defined by charging of the delay means to a response value. A discharge circuit of the delay means is conducted through the first switch.
The synchronous control of the charging switch dependent on the voltage at one of the switches of the inverter according to the above described circuit has the particular and significant advantage that the operating status of the step-up regulating unit automatically depends on the status of the inverter. When the inverter is shut down, for example given a malfunction of the load connected to it, then the step-up regulating unit is also automatically shut down and energy is no longer pumped into the inverter. On the other hand, the step-up regulating unit starts automatically with start-up of the inverter.
Since the duration of current flow over the charging switch in the above described circuit also depends on the voltage at the charging capacitor, the power supplied by the step-up regulating unit also changes automatically when the output voltage of the inverter is varied in order, for example, to change the lamp power. It thus suffices in order to change the lamp power to perform an operation on the inverter, for example to change its operating frequency or--given a constant operating frequency--to change the drive times of the switches of the inverter.
Finally, the inverter can also be operated with d.c. without any commutation whatsoever, whereby all of the enumerated advantages are retained.